This renewal application requests funds to continue development of a catheter tip device to measure instantaneous volume blood flow using ultrasound. The instrument consists of two components: apparatus for vessel cross sectional measurement by the pulse echo technique and apparatus for velocity measurement by the doppler technique. Velocity and cross sectional area, when multiplied, will give volume blood flow. During the past 16 months of funding with HE 14645, we have been able to demonstrate the feasibility of area measurement in vivo. We wish to make technical improvements in the area device, including on line processing of echoes, add the velocity component, and conduct an extensive series of tests. We then plan to make the necessary additions and modifications for clinical implementation.